The development of uncertainty over the progression of a project (i.e. dynamism) is a central issue in engineering management; however, it has been little explored. This paper answers the question of how uncertainty develops over the course of complex engineering. We present a case of a renewable energy power plant where we performed content analysis on over 54,000 e-mails. The findings reveal a new mechanism affecting uncertainty development. We call this mechanism ‘uncertainty masking’ and define it as: the process through which a ‘root uncertainty’ is misidentified by the project team, resulting in the creation and management of a ‘symptomatic uncertainty’. Root and symptomatic uncertainty types compound over time and hamper uncertainty resolution, leading to growth in level of uncertainty during later project stages. We describe the impact of uncertainty masking on the u-shape level of uncertainty in the case project. This research contributes to the engineering-management literature by explaining observations of uncertainty growth, which existing theory is unable to explain. We thus significantly advance uncertainty theory in engineering management.